254 PROCEEDINGS OF THE AMERICAN ACADEMY, 



38, 42-44, 47) in which only two or three of the cells of an organ had 

 taken the stain, and that not too intensely, thus allowing the two poles of 

 the cells to be traced, — the peripheral pole through, or partly through, 

 the cuticula, the central pole for some distance toward the central ner- 

 vous system. 



(4) Conclusions as to Finer Structure of Sense Organs. 



From the study of a large number of preparations made by the differ- 

 ent methods described, I have reached these conclusions. 



(1) That epidermal sense organs composed of a number of sense cells 

 are present in all parts of the integument of the Maldanids, Clymene 

 producta and Axiothea torquata, and that in certain regions of the worm 

 these sense organs show a definite arrangement into groups and zones. 



(2) That the cells of these sense organs are elongated, spindle-shaped 

 cells, — bipolar nerve cells of the type described by Retzius ('92, '92*, 

 and '95) for the isolated sense cells of Nereis. 



(3) That these bipolar cells differ much in the distance of the nucleus 

 from the cuticula. 



(4) That there are a considerable number of such bipolar cells in 

 each sense organ, although in many cases only one cell takes the stain. 

 In almost all cases in which only one cell is stained, the peculiar contours 

 of the cuticula in sections give satisfactory evidence of the presence of 

 a multicellular sense organ. 



(5) That each of these cells possesses at its exterior end a sense hair. 

 These hairs I believe capable of retraction below the cuticula, although 

 I cannot offer conclusive evidence upon this point. 



(6) That the deep portion of each of these cells is much more slen- 

 der than the peripheral portion, and turns at an angle beneath the epi- 

 dermis toward the central nervous system. But not all the processes 

 from the central ends of the cells of an organ pass in the same direction. 

 I have seen them in some instances separate when near the base of the 

 epidermis, and diverge until they took opposite directions (Plate 6, 

 Fig. 42), in which they could be followed for some distance. This 

 would seem to indicate that nerve fibres from the same sense organ may 

 enter the central nervous system from opposite sides. The exact man- 

 ner in which the nerve fibres from these sensory cells enter the central 

 nervous system I have not been able to observe. 



(7) That the direction of the cells of the sense organs in reference to 

 the cuticula varies considerably. As a rule, the long axis of tlie cell 

 body is nearly perpendicular to the cuticula, and to the circular muscles. 



